Increasing speed in xeroradiography



OCL 14, 1958 R. G. VYVERBERG v 2,856,535

INCREASING SPEED IN XERORADIOGRAPHY Filed May 31, 1957 15 |0 I6 FIG. 1

INVENTOR. FIG. 5 Robert G vyverberg if y BYTQ (296e l ATTORNEY United States Patent O 2,856,535 l INCREASING SPEED IN XERORADIOGRAPHY Robert G. Vyverberg, Pittsford, N. Y., assignor to Haloid Xerox Inc., a corporation of New York Application May 31, 1957, Serial No. 662,817 7 Claims. (Cl. Z50- 65) This invention relates generally to xeroradiography and, in particular, to techniques of image intensification in connection with the production of radiographs through electroradiography.

In ordinary lm radiography, the general accepted practice is to place the ilm between intensifying screens, either of heavy metal or of a lluorescent type, which are placed in very intimate contact with the film. While it is possible to place insulating intensifying screens directly in contact with the xeroradiographic plate, it is unsatisfactory, since there is distortion of the image because of current flow either while they are in contact or during removal, and because it is a troublesome operation both to apply the intensifying screen after sensitization and remove before development.

Now, in accordance with this invention, particulate material which acts to intensify the image is deposited directly on the surface of the plate member. The sensitive plate is then exposed and developed while theparticulate material remains in position. This results in improved intensication and improved resolution over the prior art techniques, and at the same time uncontrollable discharge does not take place.

To further understand these broad objectives of the present invention as well as other objectives and advantages of this invention which will be more apparent in View of the following description, reference is had to the attached drawings, wherein:

Figure 1 illustrates a flow step of placing an electrostatic charge on the surface of a plate member employed in one embodiment of this invention.

Figure 2 illustrates the liow step of particle deposition to create a particle intensifying layer.

Figure 3 illustrates exposure to a pattern of penetrating radiation.

Figure 4 illustrates development of the electrostatic image created, for example, through the ow steps illustrated in Figures 1, 2, and 3.

Figure 5 is an enlarged fragmentary illustration of the imageI appearance following development as illustrated in Figure 4.

For a better understanding of this invention, reference is now had to Figure 1 wherein a plate generally designated comprising a normally insulating layer 16 overlying a conductive backing member is electrostatically charged by corona discharge electrode 13 supplied with a high potential from high voltage source 12. Backing 15 of plate member 10 is, as illustrated, held at a ground potential.

Charging of plate 10 may be carried out according to any known technique and using any known charging device or system. For example, the techniques and devices disclosed and described in Walkup U. S. Patent 2,777,957, Mayo U. S. Patent 2,778,946, Walkup U. S. Patent 2,774,921, or the like may be employed. The intent in connection with the flow step illustrated in Figure 1 is to deposit a` substantially uniform electrostatic charge across the surface of plate 10 and any means or method of accomplishing this end purpose is intended to be included herein.

Plate 10 is a conventional plate used in the art of xeroradiography and, thus, includes plates generally used in xerography. Layer 16 should be composed of a material which becomes conductive when exposed to penetrating radiation and which in the absence of penetrating radiation is a good insulator. Such a material has been and will be referred to in the specication and claims as normally insulating and includes material which generally have a resistivity in the order greater than 1012 ohm-centimeters in the absence of radiation and a resistivity in the presence of penetrating radiation of about at least 103 or 104 ohm-centimeters lower than in the absence of such radiation. Typical materials which may comprise a normally insulating layer according to this invention include amorphous or vitreous selenium, sulphur, anthracene, photoconductive materials in binders as, for example, Zinc oxide in a silicone or resin binder ortho like, some of the phosphors, and the like. It is to be understood and realized that the materials listed are included only for illustrative purposes of the many that may be employed, and it is intended to encompass within the scope of this invention those materials having the insulating and conductive characteristics described above. The backing member 1S may comprise any conductive layer such as aluminum, brass, or the like. This layer may also comprise a resistive material impregnated with conductive particles to result in conductivity of the layer as, for example, treated paper or the like. Generally, rigidity in this layer is preferred to enable positioning of the object being examined in Contact with plate 10 and rigidity in this layer will generally supply sufcient strength to support the object being examined or allow the object to rest on the plate. Generally also, a selenium layer is preferred to be used as the normally insulating layer 16 in carrying out this invention, and the selenium employed may be of the light sensitive, X-ray sensitive variety or the light insensitive, X-ray sensitive variety.

Reference is now had to Figure 2 wherein deposition of a substantially uniform particle layer on the surface of plate 10 is illustrated. In this figure plate 10 comprising backing member 1S and normally insulating layer 16 is placed face down on developing box 20. Developer supply 22 produces a cloud 21 of particles in gas suspension within development box 20. The particles making up cloud 21 are preferably electrostatically charged to a polarity opposite to the polarity of charge placed on the surface of normally insulating layer 16 in the flow step of Figure 1. However, it has been found that, without charging the particles, a substantially uniform layer of particles is deposited on the surface of normally insulating layer 16, and it is presently believed, without intending to state a specic theory of operation or a limitation on this invention, that deposition of uncharged particles takes place due to induction of opposite charge in the particles as they contact the plate surface. Using charged particles, however, results in a more uniform particle layer than if uncharged particles are employed, and uniformity in the particle layer is desired according to this invention.

The particles deposited in accordance with the illustration in Figure 2 may comprise standard, X-ray, fluorescent powders, for example, barium platinocyanide or calcium tungstate powders. Other fluorescent or phosphorescent powders as, for example, zinc oxide, calcium tungstate, Zinc salt of 8-hydroxyquinoline, or the like may also be employed. Alternatively, insulating particles of a material having a high atomic number such as heavy metal compounds or insulating coated` conductive particles of heavy metal or heavy metal com- Patented Oct. 14, 1958 pounds may be employed. Characteristically, the particular material employed and the layer it forms should be electrically insulating. Also, the layer should be one that will produce an intensifying effect when exposed to a radiation pattern. When heavy metals or heavy metal compounds other than fluorescent or phosphorescent materials are employed intensification is effected through the release from the particles of secondary X rays or electrons. These materials are used when high energy radiation is employed and may be used with either a light sensitive or light insensitive plate. When, however, low energies are being employed, uorescent or phosphorescent materials which will glow under X-ray excitation are preferred and intensification is effected, in addition to the secondary X rays or electrons released from the particulate material, by the light glow in the particulate material brought on by X-ray excitation. Preferably when employing fluorescent or phosphorescent material, the material should be chosen because of its fluorescent or phosphorescent output as the output relates to the spectral response of the plate in order to assure eciency during exposure.

The cloud generator and the development box to deposit the particulate material on the surface of plate may comprise one as simple as the illustration in Figure 2 as, for example, an atomizer loaded with the particulate material and feeding into an enclosure. It may also, for example, comprise a device of the type illustrated and described in Phillips U. S. Patent 2,711,481 or Landrigan et al. U. S. Patent 2,725,304 or Kaiser U. S. Patent Serial No. 492,003, now U. S. Patent 2,792,971 or Andrus et al. U. S. patent application Serial No. 504,726, now U. S. Patent 2,815,330 or in my issued U. S. Patent 2,759,450.

The plate 10 is sensitive to light following charging as illustrated in Figure l if of the light sensitive variety as, for example, where a light sensitive selenium layer is employed as normally insulating layer 16. Accordingly, if light sensitive, following charging it is shielded from light as, for example, by placing a dark slide, shield, or the like over the light sensitive layer 16. The shield or slide is removed during particle deposition as illustrated in Figure 2. Following particle deposition the plate member continues, if originally light sensitive, to be sensitive to light and, accordingly, is again shielded 'from light and is moved into position for exposure illustrated in Figure 3.

In Figure 3 exposure of a sensitive plate carrying a particle layer as described above in connection with Figures l and 2 is exposed to a radiation pattern. The plate generally designated 10 comprising normally insulating layer 16 overlying conductive backing member 15 is in this embodiment positioned within frame 17 and shielded from light by shield 18. Across the surface of normally insulating layer 16 is a substantially uniform layer 11 of particles 23. These particles 23 comprise the particles which have deposited across the surface of normally insulating layer 16 in accordance with the procedures described ink connection with Figure 2. Shield 18 preferably comprises a thin layer of aluminum or the like which will have little or no stopping efect on the penetrating radiation directed through to plate 10 but may comprise a layer which acts to lter the radiation directed to plate 10 as, for example, a heavy metal layer, or the like. Positioned on shield 18 is an object 25 being examined and above the assembly of plate 10 in frame 17 supporting object 25 is X-ray source 26. X-ray source 26 may comprise an evacuated envelope containing a heavy metal anode and a heated lament supplied with an external source of potential as is commonly used in the art to generate X rays or other X-ray source as, for example, radium or cobalt 60 may be used. The illustration in this gure is intended only to illustrate an X-ray source, and various known sources may be employed in carrying out this invention.

The object 25 illustrated as being examined in this iigure comprises a shell having two faults 27 illustrated in this figure as -bubbles and generally referred to in the art as voids within the high explosive within the casing. It is apparent, however, that object 25 is included herein for illustrative purposes only and that objects and faults other than those illustrated may be examined according to this invention.

Exposure of the object and plate 10 to radiation from source 26 is continued for a period of time depending on such factors as the intensity of radiation issuing from source 26, the density of object 25, and the like, as is well-known in the art. Following exposure, plate 10 is exposed to developing particles as is illustrated in Figure 4.

Referring now to Figure 4, there is illustrated a developing device of the type 'fully described in my U. S. Patent 2,759,450. As illustrated in this figure, a cloud generator 28 feeds cloud 21 into housing 20 on which is positioned plate 10 comprising backing member 15 and normally insulating layer 16 carrying across its surface particles 23 in a substantially uniform layer. Cloud 21 is created in housing 20 as is described in my aforementioned patent and particles of cloud 21 deposit on particles 23 overlying normally insulating layer 16 in conformity with the radiation pattern to which plate 10 was exposed as illustrated in Figure 3 and result in a developed image as is illustrated in Figure 5. The developer particles used in development in Figure 4 are of a contrasting color to the original color of the particles deposited in accordance with the illustration in connection with Figure 2.

Various known developers in the art of xeroradiography may be used as, for example, a mixture of Malachite Green and the zinc salt of S-hydroxyquinoline in a suitable resin binder or a mixture of Prussian Blue and the zinc salt of S-hydroxyquinoline in a suitable binder, other dyes in resins, and the like. These various color developers would be used where the first development step involved development with a particle material 23 comprising a white or light color iluorescent or phosphorescent material or heavy metal or metal compound. If a dark material is employed for particles 23 during the iirst development step illustrated in Figure 2, then a light contrasting color developer may be used during the second development illustrated in Figure 4. Such light developer materials which have been employed include, for example, calcium carbonate, zinc oxide, and the like.l

Reference is now had to Figure 5 wherein there is illustrated an enlarged fragmentary view of a developed image according to this invention following steps described in connection with Figures 1, 2, 3, and 4. In this figure there is illustrated a portion of object 25 developed on the surface of normally insulating layer 16. Along the entire surface of normally insulating layer 16 there is deposited particle layer 11 comprising particulate material 23 in a substantially uniform layer. Deposited on top of layer 11 made up of particles 23 are particles 30 of a `contrasting color to particles 23. Particles 30 deposit in accordance with the charge pattern 'formed following exposure illustrated in Figure 3 and define object 25. Faults 27 are apparent in the radiograph produced following `development in Figure 4 through the contrast of particles 23 and particles 30 and due to the fact that substantially no development during the second development (Figure 4) will take place in the area of the faults on the surface of normally insulating layer 16. Thus, in this area particles 23 deposited during development in Figure 2 show up and define the faults 27 in object 25 examined in Figure 3.

Various techniques of development are known in the art of xerography and can be employed in this invention as, for example, a reverse form of development to the one illustrated in Figure 5, and in such event faults 27 as well as the background areas (i. e., areas over which there was no object) would be developed with a relatively dense layer of particles 30, whereas all other areas of object 25 would remain relatively undeveloped thus bringing up the voids in object 25.

The image, once developed, may be viewed in apparatus as, for example, illustrated and described in connection with Mayo et al. U. S. Patent 2,771,002, may be transferred to another surface, or the like as is well-known in the art of xeroradiography.

The image pattern for development is formed during exposure in accordance with techniques illustrated in Figure 3 and is presently believed to result due to the selective dissipation of charge from the surface of normally insulating layer 16 and through normally insulating layer 16 to conductive backing member 15 in areas affected by the pattern of radiation striking normally insulating layer 16. Although some charges even in exposed areas will tend to adhere to the surface and be bound to the deposited particulate material 23, the major portion `of the charges in exposed areas will flow through to the conductive backing member thereby to a large extent discharging charge 'from the surface in exposed areas. There thus results an electrostatic charge pattern on the surface of normally insulating layer 16 which may be developed through the deposition of charge particles as illustrated in connection with Figure 4 to result in a reproduction as illustrated in Figure 5.

Although in Figure 1 charging of the surface has been described as taking place prior to the deposition of a substantially uniform layer of particles across the surface of the normally insulating layer, it has been found that a layer of particles can be deposited on the normally insulating layer without previously charging this layer by feeding the particles as through the use of a powder cloud into contact with the layer whereat they tend to deposit. It is not presently known whether these particles tend Ito adhere due to charges induced in the surface by the particles themselves or due to other phenomena. However, generally, in order to assure a substantially uniform and dense layer of particles following development as illustrated in Figure 2, it is preferred to charge the surface of the normally insulating layer as illustrated in Figure 1 prior to the first development step. If however, charging of this layer does not take place prior to the first development step illustrated in Figure 2, then charging as illustrated in Figure l is necessary after the development step illustrated in Figure 2 prior to exposure to a radiation pattern as is illustrated in Figure 3. Exposure in such event, it is believed, results in a charge flow through the normally insulating layer and to its surface to bind charges on the particulate material 23. The disadvantage with this technique of image formation is that the particulate material 23, even when distributed in a substantially uniform layer, is somewhat irregular, and charges deposited on the particulate material do not create as uniform a field of force through the normally insulating layer 16 and to the backing member 15 as do the charges deposited on the uniformly thick normally insulating layer 16. Accordingly, in carrying out this invention according to the preferred embodiment, charging as illustrated in Figure 1 takes place prior to the deposition of particulate material 23 in a substantially uniform layer 11 across the surface of normally insulating layer 16.

' The radiograph produced according to this invention is viewed conveniently and easily with layer 11 present, and

a high contrast and high resolution print results. The intensifying layer 11 also aids to decrease the time of exposure necessary to produce a valuable image for development purposes and, accordingly, further improves upon the art of xeroradiography.

While the present invention as to its objects and advantages as have been described herein has been carried out in specific embodiments thereof, it is not desired to be limited thereby but is intended to cover the invention broadly within the spirit and scope of the appended claims. r

What is claimed is:

1. The method of producing an improved Xeroradiograph on the surface of a xeroradiographic plate comprising a photoconductive insulating layer overlying a conductive backing member, said method comprising depositing a uniform electrostatic charge across the surface of the photoconductive insulating layer of the xeroradiographic plate, depositing on the surface of the` electrostatically charged photoconductive insulating layer a uniform intensifying layer of insulating particulate material chosen because of its intensifying effect on said photoconductive insulating layer when an image pattern of radiation passes through said intensifying particulate material, exposing the photoconductive insulating layer carrying across its surface the layer of intensifying particulate material to an image pattern of radiation to thereby form an electrostatic latent image pattern on said photoconductive insulating layer of said radiation pattern, and while said particulate layer remains in position on said intensifying photoconductive insulating layer developing the electrostatic latent image with a developer material of a contrasting color to said particulate layer previously deposited on said photoconductive insulating layer.

2. The method of claim 1 in which said intensifying particulate material employed during the first deposition step comprises a fluorescent material.

3. The method of claim 1 in which said intensifying particulate material employed during the first deposition step comprises a phosphorescent material. 4

4. The method of claim 1 in which said intensifying particulate material employed during the first deposition step comprises a material of high atomic number.

5. The method of claim 1 in which said photoconductive insulating layer of said xeroradiographic plate comprises a uniform layer of amorphous selenium.

6. The method of claim 1 in which said intensifying particulate material deposited in a substantially uniform layer across the uniformly charged photoconductive insulating layer is electrostatically charged prior to 'being fed for deposition purposes to the plate surface.

7. The method of claim 1 in which said intensifying particulate material employed during the first deposition step comprises insulating coated conductive particles of heavy metal. v

References Cited in the file of this patent UNITED STATES PATENTS 2,666,144 Schalfert et al. Jan. 12, 1954 2,681,473 Carlson June 22, 1954 2,809,294 Vyverberg Oct. 8, 1957 2,817,767 Rosenthal Dec. 24, 1957 OTHER REFERENCES McMaster: New Developments in Xeroradiography, article in Non-Destructive Testing, summer number 1951. 

